Successful fertilization, completed when parental genomes unite within an activated oocyte, is critically important for efficient reproduction. Investigations on the microtubule configurations in bovine and porcine zygotes have led to the discovery that the sperm contributes the centrosome during fertilization in these domestic species. In addition, we have demonstrated that sperm from breeding bulls vary predictably in the ability to organize microtubules after sperm incorporation, and that variations in sperm centrosomes affect the outcome of fertilization. The goals of this project are to characterize, at the molecular level, the relative parental contributions to the bovine zygote=s centrosome during fertilization. We have two aims for this project. Aim 1. Is the recruitment of maternal molecules to the sperm centrosome essential for the completion of fertilization? Aim 2. What is the molecular basis of the motility which unites the male and female pronu clei ? The information obtained during these experiments will add to our fundamental knowledge about the molecular mechanisms leading to pronuclear apposition and genomic union during fertilization in cows, a key step in the reproductive process of all animals. Furthermore, it holds promise for novel assays to test male reproductive function in potential breeding studs. This research may also uncover a new site at which to assay for compounds affecting fertility, with applications for fertility assessment, reproductive management, and reproductive toxicology, as well as aid in developing new approaches for improving reproductive efficiency in domestic species. FUNDING USDA 9702358 PUBLICATIONS Sutovsky P, Simerly C, Hewitson L, Schatten G. Assembly of nuclear pore complexes and annulate lamellae promotes normal pronuclear development in fertilized mammalian oocytes. J Cell Sci 111:2841-2854, 1998.